How sensors can detect the crime-solving clues at our fingertips

Currently, traditional methods of fingerprinting don't allow forensics experts to differentiate between prints at a crime scene left before and after the crime has been committed, or to differentiate important or interesting prints from background "clutter" (ie very old fingerprints). Current methods (including "dusting", chemical and computer analysis) also take a long time to process and risk contaminating vital DNA evidence contained in fingerprints during, for example, chemical processing.

The application of Electric Potential Sensors (EPS) technology to forensic fingerprinting is one of numerous applications being investigated by its developers, Professor Robert Prance and his research team in the University's Centre for Physical Electronics and Quantum Technology.

Experiments involving EPS scaled down to microscopic level showed that it might be possible to accurately date and identify the electrical imprint left behind in a fingerprint without interfering with any other evidence the fingerprint might reveal.

The findings are now published in the journal Forensic Science International.

The sensors work by detecting extremely low-frequency electrical activity over a distance of 5 microns (one micron being equal to one millionth of a metre).  This microscopic scale and sensitivity allows the sensor to map a high-resolution image of electrical charge that occurs over the surface of a source material (for example a human finger), when it makes contact with a thin insulating surface (ie a plastic surface). The trace of this electrical charge left behind in the fingerprint is imaged using an electric field microscopy system.

The technology offers two significant advantages over traditional fingerprint analysis:

• As the finger print ages, the electrical activity decays, sometimes over a period of days, allowing scientists to date the print and compare that to the estimated time of the crime. This ability could have important implications in the elimination of suspects, for example.

• The non-invasive nature of the technology means that biological material in the print is not destroyed by chemical processing and can still be harvested for DNA analysis. It would also allow the analyst to harvest material selectively, potentially saving time by avoiding indiscriminate DNA analysis of all prints in a given area.

Professor Prance says: "In its present form this technique could be used in forensic laboratories now and with the development of arrays of sensors could easily become field deployable in the near future."

More information: 'Imaging electrostatic fingerprints with implications for a forensic timeline, Philip Watson, Robert Prance et al, Forensic Science International DOI: 10.1016/j.forsiint.2011.02.024

Provided by University of Sussex